Learning From the Swinging Bridge

What rickety, rural suspension bridges can teach us about modern infrastructure. An Object Lesson

Ilya Naymushin / Reuters

Back in the day, people in the valley of Virginia who lived across the river from town generally crossed by a “submarine” bridge, a roadbed set a few feet above normal water level. Overwashed and impassible in flood times, it was often supplemented by a swinging bridge—a narrow, spindly structure high above the water which, as the name implies, moved beneath the feet of its users.

Rural swinging bridges were (and still are) vernacular architecture based on local knowledge and materials, but technically, they are suspension bridges just like the Golden Gate. The engineering principle is simple and sound: Anchor cables to a heavy foundation on either end, raise them near the anchor point to a height that keeps the low point of the cable’s sag just above the level of the bridge deck, then add a treadway with safety siding. Despite their tendency to swing alarmingly over swirling waters, swinging bridges are  remarkably stable. Thanks to their flexibility, they can withstand forces that more rigid structures cannot unless supported by far greater mass. A swinging bridge is low cost, easily made from local materials, and requires no superstructure built into the river bed itself.

Swinging bridges in the Appalachians were part of a private infrastructure that enabled access to small mountain coves and to large flat acres of rich bottom land, such as those horseshoe shaped farms on the famous “seven bends” of the Shenandoah River. The rickety feeling of these bridges demands a trust from the traveler that seems undeserved. Maintenance was also private—and sporadic, at best—making a venture out onto the treadway demand caution.

In Indiana Jones and the Temple of Doom (1984), Steven Spielberg happily exploits  swinging bridge anxiety. Indy and his companions cross a high Himalayan chasm on an old, ill-repaired bridge that, as the audience well knows, will either collapse or be cut loose, leaving our hero dangling precipitously. Spielberg’s setting is appropriate even if his staging is outlandish. The Himalayas are indeed home to swinging bridges, many in high mountain gorges.

Unlike the Shenandoah Valley where they serve as an emergency substitute for an extant but vulnerable transportation system, Himalayan swinging bridges are often the only way in and out of an area. In those mountains, transportation is difficult and tenuous. Paths are subject to slips. The bridges are constructed from the materials and knowledge available, and maintained by the local population. Even bridges serving the main routes between villages often have treadways with broken, missing, or rotten boards, demanding careful, often hesitant stepping and which may explain why those bridges are often festooned with strings of flapping prayer flags.

Early in the 20th century, James Burtton bought farmland along the Tokumaro River on the North Island of New Zealand. Isolated from transportation routes and therefore unable to bring his farm products to market, he built—by hand—a nearly five kilometer track from his station to the road. His house was also isolated, having been built on the east side of the river while his livestock grazed on the west. Ever the intrepid Kiwi, Burtton constructed a swinging bridge that provided both his livelihood and the cause of his death. In 1941, one of the cables gave way as he crossed the bridge, and he fell to the rocks below, breaking his leg and sustaining other injuries. He spent twelve hours crawling to his neighbor’s house, only to die soon after.

Swinging bridges remain a common feature of the New Zealand landscape, but today most are maintained by the Department of Conservation and built to fairly standard specifications. In additional to suspension cables made of steel, most have three lower cables spaced by metal bars and covered by a layer of chain-link fencing to serve as the treadway. The anxiety these bridges produce arises not from worries about their structural integrity, but instead by virtue of their locations—often set high above rushing waters linking sheer rock faces. Getting on and off of them can be more frightening than crossing. However the narrow treadway does make for lateral swinging which is usually dampened by diagonal cables anchored about a third of the way across.

Still, trust even in this standardized construction technique and maintenance can be misplaced, something learned by four French hikers in September of 2015. A short video made by one while crossing the Hopurahine Bridge on the Lake Waikaremoana Great Walk shows the bridge making a sudden lateral twist, flipping the treadway over to the hikers’ left, pitching them over the right side of the cable railing, and depositing them in the water below. The bridge then snapped back almost as if nothing had happened.

Unlike Burtton, the hikers were unharmed. Of course the Department of Conservation did an immediate study of the cause and inventoried the many bridges in their purview, but that doesn't dampen the frisson experienced almost daily by trampers across the country, particularly at that inevitable point on the bridge where there is transitory transverse movement—always cause for white knuckles and mumbled profanity.

While Burtton was building and farming, in New York City a young poet named Harold Hart Crane was trying to comprehend perhaps the greatest swinging bridge of them all—the Brooklyn Bridge. The introduction to his epic poem The Bridge is all about trust, anxiety, and embodied experience. Crane, the wanderer of Brooklyn and its bridge, opens by setting up an opposition between a scene seen and one lived. After invoking a transcendental image of birds, sails, and, by implication the soaring of the bridge, an elevator drops the speaker, presumably to a darkened theater:

I think of cinemas, panoramic sleights
With multitudes bent toward some flashing scene
Never disclosed, but hastened to again,
Foretold to other eyes on the same screen

The commonality of shared visual experience, the product of “panoramic sleights,” is a profound drop from the individual physical experience of bridge crossing, or even failing to cross as this stanza is followed by an escaped “bedlamite” whose body plummets from the bridge, “shrill shirt ballooning.” The scene prefigures Crane’s own 1932 leap off the stern of the SS Orizaba to his death in the Gulf Stream waters. The poet struggles with the impossibility of reducing the experience of his swinging bridge to a visual image. Its essence, like all swinging bridges, is in the crossing, the rocking, the trust, and the possibility of failure.

Eight years after Crane’s death and one before Burtton’s, the newly opened Tacoma Narrows Bridge, christened the “Galloping Gertie” by the men who built it, collapsed in spectacular fashion during a mildly windy day. Briefly the world’s third longest suspension span, the Tacoma Narrows’s collapse was initially thought to have resulted from the mechanical resonance of a high wind environment. Later, the true cause was determined to be aeroelastic flutter. The wind initiated a twisting of the bridge’s deck, which ratcheted up into a self-generating and rapidly increasing vibration that degraded the entire system.

Although the Tacoma Narrows bridge’s twisting was extreme, for walkers of rural swinging bridges, it’s an eerily familiar movement. Galloping Gertie mimics the motion that produces that moment of panic felt by anyone crossing a swinging bridge—first a movement up and down later accompanied by pitch, then roll and maybe a little yaw, a complicated dance that feels out of control. The Tacoma Narrows collapse alerted bridge engineers of the to the need to account for aerodynamics and aeroelastics in bridge design, but more broadly it raised questions about trust in large scale infrastructure. Confronting an old, decayed swinging bridge in Nepal or Virginia inspires obvious caution, care, and attention in the traveler. Such concern is built into the very nature of the bridge. Large-scale modern architecture effectively dampens that concern even as it dampens wind effects.

Most bridges in the industrial West tend not to move much. Usually crossed in cars, it is unlikely that travelers can even look up to see the “cables breathe the North Atlantic still,” as Crane said of the Brooklyn Bridge. Instead bridges are simply part of a longer, smoothly paved road, and part of a larger, generally unthought structure underpinning quotidian existence. Unless you are a poet, a painter, or a homeless person, you will not likely notice the “choiring strings” above or the slowly rusting, crumbling structure below. And so, the vernacular swinging bridges that remain now carry another weight. They bring us back to ground. By their very nature as footbridges, they are part of a slow infrastructure, one that reminds users that all infrastructure, no matter how sleek, modern, and fast, is still made of matter to be reckoned with, understood in their local circumstances, treated with care, and ignored with some peril.

This article appears courtesy of Object Lessons.